COLOGNE (Reuters) - The acting head of Europe's aviation regulator said on Wednesday the agency would halt its indirect approval of Boeing's jet production if warranted, but he feels reassured that the planemaker is tackling its latest safety crisis.

In an interview with Reuters, the European Union Aviation Safety Agency's acting executive director, Luc Tytgat, gave the first public indication that international cooperation underpinning global airplane production was being tested by the ongoing crisis as it rarely has been.

Asked if EASA would be prepared to stop recognising U.S. production safety approvals declaring that Boeing jets are built safely, Tytgat said, "If need be, yes".

Boeing has been under mounting pressure over factory quality control since Jan. 5, when a door plug tore off a 737 MAX 9 jet in mid-air in an incident blamed on missing bolts.

The U.S. Federal Aviation Administration said last week an audit of Boeing and supplier Spirit AeroSystems found multiple instances of poor controls.

Under a transatlantic pact, the FAA and EASA regulate the factories of their respective planemakers - Boeing and Airbus - and recognise each other's safety approvals.

However, if one side loses confidence in the other's compliance checks, it can call for consultations and, if those fail, suspend recognition after a pause of 30 days.

Such steps are rare.

"All the tools must be implementable as soon as we see the justification or situation that requires us to take appropriate measures," Tytgat said, adding that no such action was imminent.

EASA's influence over the design of Boeing planes has grown following the MAX crashes, but it has relatively few ways to increase its monitoring of the production of existing Boeing models other than the drastic option of suspending recognition.

Pressed on what would push EAA to go that far, Tytgat said, speaking only for himself, "More fatal accidents in the future".

The FAA did not comment directly on the EASA remarks but a spokesperson reiterated the agency's earlier statements that Boeing must commit to "real and profound improvements".

Boeing did not comment.

'REASSURED' AFTER BOEING MEETING

But Tytgat did not see any immediate threat to Boeing's production certification.

"We don't see why (it) cannot be maintained today. It is more (about) the oversight and monitoring conditions that are in place."

Tytgat said he held a discussion with senior Boeing executives on Friday that were reassuring.

"I have seen a change in the management. They put a lot of weight on quality controls, product quality and I was really reassured about the willingness of the top management to change .... production quality control," he said.

EASA officials visited Boeing's 737 plant last week, he said. But Tytgat ruled out a permanent presence, saying it would "not be in the spirit" of the transatlantic safety agreement.

FAA Administrator Mike Whitaker said on Monday that the agency would take action if it saw a reason to halt Boeing production.

A decision by either of the world's two most powerful aviation regulators to upend production approval of Boeing or Airbus jets would take the safety crisis into uncharted territory and likely stir political reactions, experts said.